OK. This is much more clear. So, now I would like to better understand
Gary's side on this issue.
michael
On Fri, 21 Nov 2008 13:43:44 +0100
Christian de Sainte Marie <csma@ilog.fr> wrote:
>
> Dave,
>
> thanx for the clarification.
>
> Here is how I understand PRD needs, at this point. Please, all, complete and/or correct me:
>
> 1. Production rules needs subclass relationships. But in most, if not all, cases, the class hierachy is fixed and there is, therefore, no need to test it explicitely. However, it may be used by classification tests, and it is, thus, needed in the semantics. Since it is, in most, if not all, cases, externally defined, it has to be imported. But the import can be specified without requiring that subclass relationships be explicitely asserted in rules or facts.
>
> Hence, (my current understanding is that) PRD can do without ## in the concrete syntax.
>
> So, it would be interesting to challenge that assertion:
>
> 1a. What would be an use case where a subclass relationship test would need be explicit in the condition of a rule (as opposed to the test being carried silently as a consequence of importing the class hierarchy)?
>
> 1b. What would be an use case where a subclass relationship would need be explicitely asserted in a fact (as opposed to being taken into account as a consequence of importing the class hierachy)?
>
> 1c. What would be an use case where a subclass relationship would need be asserted as a consequence of a rule (as opposed to the class hierachy being immutable)?
>
> 2. Production rules need to test membership relationships, though. But in most, if not all, cases, class membership is immutable. So that class membership needs be asserted only at an object's creation. It can thus be part of the semantics of the creation action (e.g. as proposed in [1]).
>
> Hence, (my current understand is that) PRD can do with # being allowed in tests and variable bindings only.
>
> The only challenge to that assertion that I can imagine would be an use case for class membership assignement or mutation as a consequence of a rule (but you all know how poor my imagination :-)
>
> 2a. What would such an use case look like?
>
> 2b. Other ways to challenge the assertion, anyone?
>
> Dave Reynolds wrote:
> >
> > The proposal we discussed some weeks ago (but seem never to have
> > formally adopted) was to only have # and only in rule conditions. That
> > is appealing to be me because then I don't have to implement anything
> > (if you can't assert data you can't test it!).
>
> The semantics of PRD is specified with respect to a data source. But, as far as I understand, it does not require the data to be explicitely asserted as facts (as opposed to being imported by reference to the data source). So that, as soon as we will have specified that import, it will be possible, in PRD at least, to have facts to test class membership, whether PRD allows to assert facts or not...
>
> Cheers,
>
> [1] http://www.w3.org/2005/rules/wiki/Alt_AbstrAction
>
> Christian
>
>
>